1. Field of the Invention
The invention relates to a valve, comprising a spring arrangement, intended to adjust a damping medium flow between the damping chambers of a shock absorber. The valves are preferably electrically controlled and intended for computer-controlled shock absorbers for vehicles.
2. Description of the Related Art
Spring arrangements consisting of a weak and a stiff spring, in which the weak spring biases the stiff spring and contributes to different spring qualities in different parts of the stroke, are used in many technical constructions, such as, for example, in valves intended to control the damping medium flow in a vehicle shock absorber. Especially in shock absorber applications in which the valves must have a precise damping pressure level without being adjustable, a low spring constant right at the start of the stroke is important. The low spring constant then passes into a higher spring constant, which is matched to the high pressures which can be generated in the absorber during rapid motions.
A known design within the field of the invention is described by the Applicant's published patent application WO2006145419. This patent application describes a shock absorber valve in the form of a pilot-operated two-stage valve, intended to control a damping medium flow between the two damping chambers of a hydraulic shock absorber. The shock absorber valve comprises a valve housing having at least a main valve with a movable valve part in the form of a main cone disposed between a main valve spring arrangement and a seat, and a pilot valve comprising a pilot slide. The main cone delimits a pilot chamber in the valve housing, in which pilot chamber the valve main spring and the pilot slide are disposed. The characteristics of the shock absorber valve are principally controlled by the pressure build-up in the pilot chamber, which is adjusted by the position of the pilot slide in the pilot chamber. This position is determined by the force equilibrium between the spring forces of one or more secondary springs, the pressure around the pilot slide and the force opposing these from an electrically controlled actuator.
The spring arrangement of the main valve has here been shown in two embodiments, in which the variation in length of the main spring and the accompanying variation in bias is absorbed by a further outside-situated spring in series, which has a significantly lower spring constant, so that the force variations become less due to the length tolerances of the stiff spring. In this way, an initial stroke is obtained, which operates with the spring constant of the weak spring, and a residual stroke, in which the weak spring has bottomed and the spring constant is determined by the stiff spring. Very stiff main springs have proved necessary in many of the present applications, and at the same time an extremely precise and low bias is required. This low bias has been created by the weak spring.
A further known variant for creating a low bias of the stiff main valve is to place an arched cup spring, a so-called Belleville spring, at the bottom in series with the main spring. It has been shown that such arched springs do not work well in association with the main spring because this construction gives too great a spread of the force-absorbing capacity of the springs. A spring element is also known which separately gives a low spring constant, see, for example, DE10312977A1 and U.S. Pat. No. 4,535,816A1. This spring is intended for use as a separate spring, however, and not in a spring arrangement together with a stiff spring.
For cost reasons, the valve housings against which the springs rest need to be formed of soft and cuttable materials with good bearing capacity. This has proved to be a poor combination together with springs with high spring forces in hard spring steel, which is likely to eat into the material. This dirties the valve and gradually produces a significant reduction of the set bias force of the valve.
Moreover, the prior art is bulky and it takes up valuable volumes required for springs with high spring constant, which must have a small length and diameter. The spring arrangements in the above-described known valve technology are also unnecessarily expensive and complicated.